PHOENIX (AP) - A key portion of the Affordable Care Act rolls out Tuesday, allowing Arizonans without employer-provided health insurance to sign up for policies on a government-run exchange and check to see if some of the costs will be offset by tax credits.

The health insurance "marketplace" for Arizona will be run by the federal government because Arizona is one of roughly three dozen states that rejected the chance to run their own plans. A variety of plan levels will be available that cover basic health care needs and pay for 60 to 90 percent of the costs of doctor visits, hospitalizations and other medical services.

And people with pre-existing conditions can't be locked out of the market and won't be charged more than others their age.

Insurance premiums came in cheaper across the nation than expected, good news for the federal officials who have been touting the benefits of President Barack Obama's health care overhaul in the face of continuous Republican opposition.

"There's so much concern out there" that the government isn't up to the task, said David Sayen, the regional administrator for Centers for Medicare and Medicaid Services, which is running the insurance marketplaces. "For some reason people don't think we're capable of doing something like running big health care programs that we've been doing for 35 years."

The agency, part of the Health and Human Services administration, already provides health insurance to about 100 million people though Medicare, Medicaid and the Children's Health Insurance Program.

About 20 percent of Arizonans don't have insurance, but at least 300,000 are expected to get Medicaid coverage for the poor starting Jan. 1. That leaves about 700,000 people without insurance, many of them eligible to buy it through the exchanges.

Premiums released last week came in lower than expected, with Arizona's average rates for two lowest-cost "silver" plans that pay for 70 percent of medical costs costing $248 and $252 per month. That's before tax credits that will cut the price for lower-income residents and is substantially less than the national average of $310 or $328 for those plans.

But glitches are already evident.

Late last week, the Health and Human Services Department said a Spanish language version of the www.healthcare.gov website - where people will be able to compare plans, providers, rates and sign up for insurance - will not work for weeks. They also said small businesses that will be using a similar site won't be able to sign up for insurance until November, although they can compare plans and rates.

That is to be expected, according to Dan Derksen, a University of Arizona public health policy and management professor who helped set up New Mexico's marketplace.

"It won't go entirely smoothly. However, I think that CMS is very prepared to use feedback and information to quickly improve the system," Derksen said Friday. "This is a major undertaking and it will test the new federal data services system."

One outspoken critic of the Affordable Care Act said the rollout of the health insurance marketplaces will bring a raft of problems.

"There's so many aspects of the system that aren't functioning," said state Rep. Carl Seel, R-Phoenix. "Small businesses, they're going to be required to go into this complicated system with no benefit."

Seel said allowing insurance companies to sell policies across state lines, limits on malpractice lawsuits and reducing fraud, waste and abuse would bring better access to medical care without the burdens.

"The alternative is this novel concept called the free market," he said. "You do those three things ... and you'll go a long way toward making health care accessible and affordable."

People can expect a media blitz in the coming week, with advertising across multiple media formats and outreach ramping up in the weeks ahead to make people aware of the insurance exchange, Sayen said.

"Our product is going to be available in a week, and that's when we're going to start marketing and yelling from the rooftops and all that," he said.

The insurers available in Arizona for each of the plans won't be revealed until Tuesday, when millions of Americans who don't get health insurance at their jobs and make too much to qualify for Medicaid will be able to use the insurance exchanges to shop between four tiers of plans, plus available catastrophic coverage plans.

They can sign up as early as Oct. 1 for coverage that takes effect Jan. 1.